Rotation angular sensor with metal-injection molded magnet holder

ABSTRACT

To make it possible for a rotation angle sensor to be manufactured and assembled more easily and more accurately, the part components of a stator element ( 21 ) made of a ferritic material are held in a sintered stator body, made by a sintering technique, by at least one holding element in a holding recess of a base element made of a non-magnetizable material. A magnetic holding device ( 26, 27 ) is a holding element made by a metal injection moulding (MIM) technique with an at least partly formed magnetic isolation zone and at least one recess. An annular magnetic element ( 24 ) is attached inside the MIM holding device by means of at least one slit-shaped recess and at least one compatible linking element, and positioned at a given angle (α) in relation to a gap, between the sintered stator bodies.

BACKGROUND OF THE INVENTION

The present invention concerns an angle-of-rotation sensor with astationary component and a rotating component. The stationary componentincludes a stator accommodated in a housing with at least one base. Thestator is in two halves of ferritic material separated by space and eachprovided with at least one 45° bevel. The rotating component includes anannular magnet accommodated in a holder and rotating around the statorwith an airgap left between them.

An angle-of-rotation sensor of this genus is known from the WIPO PatentPublication No. WO A 95/14911, which is assigned to the presentapplicant. It comprises a stationary component and a rotating componentthat moves in relation to it. The stationary component has two mutuallyfacing stator halves with space between them. Each stator half is astack of sheetmetal disks secured against the bottom of the housing by atensioning component. The rotating component includes an annular magnetaccommodated in a holder.

There are drawbacks to this embodiment. The stacks are expensive tomanufacture and secure. The magnet holder is designed such that themagnet is not magnetically insulated from a shaft that the rotatingcomponent is fastened to, contaminating the outgoing signals.Furthermore, the poles of the magnet are difficult to position properlywith respect to the space between the stator halves while the sensor isbeing assembled.

SUMMARY OF THE INVENTION

The principal object of the present invention is accordingly to providea more accurate angle-of-rotation sensor of the aforesaid genus thatwill be easier to manufacture and assemble. The stationary component inparticular will be simpler, the magnet holder as magnetically insulatingas possible, and the annular magnet reliably secured in the holder andeasy to position precisely with respect to the space between the statorhalves and the stationary component.

This object, as well as other objects which will become apparent fromthe discussion that follows, are achieved, in accordance with thepresent invention, in an angle of rotation sensor of the type describedabove, by the following features:

(a) the ferritic stator halves are sintered stator halves, with at leastone holder secured in a stabilizing cutout in a baseplate ofnon-magnetic material;

(b) the magnet holder is a metal-injection molded holder with at leastone partly magnetically insulating section and with at least one cut-outgap; and

(c) the magnet is positioned in the holder by at least one cut-out gapand at least one matching web at a specified angle (α) to the space.

The present invention has several advantages. Stators are easy tosinter, precise and stable. The complicated stacking procedure iseliminated. One particular advantage is that each sintered stator halfcan be fastened to the baseplate extremely accurately. The magnet holdercan be cost effectively and, in particular, precisely fabricated bymetal-injection molding (MIM). Complicated additional shaping,especially machining, of the material is unnecessary. The holder willhold the magnet exactly where it should be within precise tolerances.Measurements will be considerably more precise. The web or space willsimultaneously position the magnet precisely in relation to the spaceduring assembly. No complicated readjustments will be necessary. It willaccordingly be possible to position the magnet's pole at a right angle,perpendicular that is, to the space between the two facing statorhalves. If any angle other than a right angle is needed in specialcases, it can be established ahead of time for all the angle-of-rotationsensors in the same series. Most significant, however, is that themagnet will be secured too tighty to turn.

Two alternative embodiments of the stator holders are possible. They canbe either sintered bolts or sintered feet. Whether bolts or feet, theycan terminate in a sintered cap. This feature ensures that the sinteredstator half is secured, stationary, in the baseplate.

The baseplate can be a stator baseplate with at least one stabilizingcutout.

Two alternative embodiments of the stator baseplate are possible.

The stator baseplate can comprise the base of the stationary-componenthousing and have stabilizing cutouts with sintered stator halves fittinginto it along with their feet and caps.

The stator baseplate can alternatively be a stabilizing disk with atleast one stabilizing cutout and at least partly surrounded by afastener with at least one fastening cutout.

At least the stabilizing disk can be at least partly surrounded by thebase of the housing.

The second embodiment of the stabilizing cutouts and the fasteningcutouts can be round or orange-segment shaped.

The stator baseplate can be aluminum, copper, or plastic.

The various embodiments of the baseplate can secure the sintered statorhalves in two different ways.

In the first approach, the halves can be sintered to final dimension,finally positioned, and forced into the base of the housing as a whole.The essential advantage of this approach is the extremely cost-effectivestabilization and fastening of the halves. The stationary component canaccordingly be finally fabricated in only two basic steps.

In the second approach, the basic components of the stator aremetal-injection molded of a ferritic material and the stator baseplatemetal-injection molded, especially of aluminum, around the stator half.The resulting blank is removed from the mold and both the half andbaseplate sintered in a furnace, both metals contracting. This processwill ensure that the half fits into the baseplate, tight and precise,and cannot be displaced by even powerful forces.

The accordingly sintered molding is then inserted into a molded housingand secured therein, either resiliently or at least to some extent byencapsulation.

The housing and its base can be of plastic, preferably injection-moldedto ensure that the stationary component constitutes a preciselydimensioned component of the sensor.

Two alternative embodiments of the metal-injection molded holder arepossible.

It can be a cup metal-injection molded in one piece of magnetic materialwith an essentially round foot, at least two, preferably cylindricalstems rising out of one edge of the foot, and an essentially round andhollow bowl resting on the stems. A one-piece bowl is considerably lessexpensive to manufacture. Such a cup can be molded of magnetic materialin a single mold. The molding will be 30 percent oversize and will needto be heated and sintered to its final dimensions. To allow at leastextensive magnetic insulation of the cup from the components to bemounted on it, the stems can magnetically insulate the foot from thebowl.

The holder can alternatively be metal-injection molded in two parts,comprising an essentially straight-sided bowl with a round base ofmetal-injection molded of a non-magnetic material, provided in a secondmolding stage with a cylindrical wall of magnetic material. Theresulting bi-material molding will be 30 percent oversize and will needto be more or less sintered to its final dimensions. The base and wallwill accordingly be precisely dimensioned and will fit togetherperfectly tightly. The wall will be precisely positioned. Thenon-magnetic material of the base will ensure effective magneticinsulation from any components to be mounted on the bowl. One particularadvantage is that the base of the bowl can be provided with a cutoutthat will readily accommodate a simply inserted valve shaft. Thisfeature will compensate for the extra expense of two-part manufacture.

A gap can be cut out of the bowl in either embodiment. If the magneticwall is provided with at least one matching web, the poles of the wallcan be positioned at a right angle, perpendicular that is, to the spacebetween the mutually facing stator halves. If, in a special case, theangle is to be other than a right angle, it can be precisely establishedfor all the products in a single series.

The web or webs can be positioned near at least one of the jointsbetween the south-north and the north-south segments of the annularmagnet. The web will accordingly be positioned in an already existinguniform magnetic-field region and will not be able to move out of themagnet's field.

The webs can be of the same material as the magnetic component they aremounted on. They can alternatively be of plastic. Plastic is to bepreferred when the magnetic component is to be fastened to the spacebetween the stator halves without detriment to the magnetic field.

For a full understanding of the present invention, reference should nowbe made to the following detailed description of the preferredembodiments of the invention as illustrated in the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic partly sectional view of a angle-of-rotationsensor coupled to a throttle valve.

FIG. 2a is a schematic top view of the stationary component of theangle-of-rotation sensor illustrated in FIG. 1.

FIG. 2b is a section along the line IIB—IIB through the stationarycomponent illustrated in FIG. 2a.

FIG. 2c is a cross-sectional view, similar to FIG. 2b, of the stationarycomponent with an attached lead frame.

FIG. 2d is a top view through the stationary component showing theattachment of the lead frame.

FIG. 2e is a cross-sectional view throughthe component of FIG. 2d.

FIG. 3a is a schematic top view of the stator baseplate in anotherembodiment of the angle-of-rotation sensor illustrated in FIG. 1.

FIG. 3b is a section along the line IIIB—IIIB through the statorbaseplate illustrated in FIG. 3a.

FIG. 4a is a schematic illustration of another embodiment of astationary component with the stator baseplate illustrated in FIGS. 3aand 3 b.

FIG. 4b is a section along the line IVB—IVB through the stationarycomponent illustrated in FIG. 4a.

FIG. 5a illustrates a magnet holder for the rotating component in theangle-of-rotation sensor illustrated in FIG. 1.

FIG. 5b is a section along the line VB—VB through the magnet holderillustrated in FIG. 5a.

FIG. 5c illustrates another embodiment of a magnet holder for therotating component of the angle-of-rotation sensor illustrated in FIG.1.

FIG. 5d is a section along the line VD—VD through the magnet holderillustrated in FIG. 5c.

FIG. 6 is a schematic top view of the space inside the stator in theadjustable magnet in the angle-of-rotation sensor illustrated in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred embodiments of the present invention will now be describedwith reference to FIGS. 1-6 of the drawings. Identical elements in thevarious figures are designated with the same reference numerals.

The angle-of-rotation sensor 2 illustrated in FIG. 1 has a stationarycomponent 20 comprising a stator 21 accommodated in a housing 23.Stationary component 20 is composed of two stator halves 21.1 and 21.2.Stator halves 21.1 and 21.2 are shaped like orange segments andseparated by space 21″. Their points are beveled, preferably 45°, at theend of space 21″. Housing 23 has a base 23″ and a cylindrical wall 23′.

As will be evident from FIG. 1, stationary component 20 is confronted bya rotating component 20′. Rotating component 20′ includes an annularmagnet 24 accommodated in a holder comprising a magnet-securingcomponent 26 and a disk-shape spacer 27. Spacer 27 is directly connectedto a throttle-valve shaft 12. Spacer 27 and stator 21 are separated,once sensor housing 23 has been secured to a housing 13 by a gap 28 androtation angle apparatus 1 in FIG. 1. Cylindrical wall 23′ andmagnet-securing component 26 are separated by another gap 29.Magnet-securing component 26 and the annular magnet 24 accommodatedtherein accordingly constitute in conjunction with spacer 27 a rotorcomponent that can rotate protected inside sensor housing 23.

Once the individual components of rotating component 20′ have beenproperly adjusted and aligned in relation to throttle-valve shaft 12,sensor housing 23 is thrust over magnet-securing component 26 along withstator halves 21.1 and 21.2 and a Hall-effect component 22 accommodatedin space 21″, leaving an airgap 25 and gaps 28 and 29. Sensor housing 23is then fastened by its cylindrical wall 23′ to valve housing 13. If thejoint between sensor housing 23 and valve housing 13 needs to be sealed,sensor housing 23 will also act as a protective jacket. The wholeangle-of-rotation sensor 2 will accordingly be protected against suchexternal conditions as the very high heat in an engine compartment andthe effects of oil, water, etc.

FIGS. 2a and 2 b illustrate one embodiment of the stationary component20 in angle-of-rotation sensor 2. The stator halves 21.1 and 21.2 aresintered stator halves 80, individually metal-injection molded of aferritic material and sintered. Since halves 80 are of the same shape,they can be fabricated continuously and sintered synchronized in batchesin a furnace. Each accordingly fabricated sintered stator half 80 willbe provided with a foot 82 that merges into a cap 81 which is secured ina stabilizing cutout 32 in a baseplate 30 of non-magnetic material, andwith a shoulder 85.

Each sintered stator half 80 will have, along with the aforesaid bevels84, a longitudinal bevel 83, also of 45°.

Two such sintered stator halves 80 can be accommodated in a single moldseparated by a space 21″, acting as a baseplate in base 23″ while theplastic sensor housing 23 is being molded. This procedure leavesstabilizing cutouts 52(32) in base 23″ to accommodate feet 82. Caps 81are also secured in base 23″. Stator halves 21.1 and 21.2 are bothsurrounded by cylindrical wall 23′ when sensor housing 23 is molded.Stabilizing components 23.1 and 23.2 each act to stabilize the apparatusby allowing the apparatus to afix itself to a corresponding femalegroove, while 21′ (FIG. 2b is consistent with FIG. 1) also allows theapparatus to be afixed, by a corresponding male attachment.

The particular advantage of such a stationary component 20 is that bothsensor housing 23 and holders and stops for stator halves 21.1 and 21.2in the form of sintered stator halves 80 can simultaneously be producedin a separate molding process, considerably decreasing manufacturingcosts and keeping the height of stationary component 20 to a minimum.

Another advantage is that Hall-effect component 22 can be positioned inthe vicinity of the densest magnetic flux near the parallel and facingsurfaces of sintered stator halves 80, while longitudinal bevels 83concentrate the flux. The enlarged space between the two sintered statorhalves 80 between the facing feet 82 in the vicinity of space 21″ keepsthe flux less dense. The transverse bevels 84 balance the flow at theorange-segment shaped stator halves due to the absence of edges.

FIGS. 3a, 3 b. 4A, and 4 b illustrate another embodiment of stationarycomponent 20.

This embodiment has a stator baseplate 40 of sintered aluminum. Itconsists of a stabilizing disk 44 that merges into an annular fastener45. Stabilizing disk 44 has a central cutout 21′ with tapering ends andconfronted by two stabilizing cutouts 42 shaped like orange segments.The are demarcated from central cutout 21′ by a cutout web 46. Annularfastener 45 includes two pairs of mutually facing fastening cutouts 43in the form of bores.

Stator halves 21.1 and 21.2 in the form of sintered halves 70 of aferritic material are sintered facing each other to the stabilizing disk44 in the accordingly fabricated stator baseplate 40. A stabilizing foot72 is sintered into each sintered stator half 70 as part of the process.The sintered stabilizing foot 72 merges into a sintered securing cap 71,anchoring the stator half into an aluminum baseplate 41 and securing itthereon. The central cutout 21′ between the two halves is as wide as itslength in baseplate 41.

This second embodiment is outstanding for strength. Sintered statorbaseplate 40 secures sintered stator halves 70 so effectively that theycan resist any static or dynamic force. Stator baseplate 40 is theninserted into a sensor housing 23 already fabricated as hereintoforespecified or otherwise.

FIGS. 5a and 5 b illustrate a magnet-securing component 26, in this casebowl 61, which together with disk-shaped foot 63 and two stems 62 and62′ constitute the entire cup 60.

Cup 60 consists of a disk-shaped foot 63 with two stems 62 and 62′extending out of it and supporting a bowl 61.

Mutually facing gaps 64 and 65 have been cut out of bowl 61.

According to the present invention cup 60 is preferably metal-injectionmolded of a magnetic material in the form of X12CrMol7Si steel. Thissteel does not corrode and is injected into a mold. The molding isheated in an furnace in a process similar to sintering, reducing thevolume of the cup by 30% to its final dimensions.

The bowl 61 in this embodiment constitutes magnet-securing component 26,and foot 63 spacer 27. Stems 62 and 62′ connect magnet-securingcomponent 26 to spacer 27 and at least extensively insulate themmagnetically from each other.

FIGS. 5c and 5 d illustrate another embodiment of a magnet holder in theform of magnet securing component 26, in this case cylindrical wall 51of metal-injection molded and sintered bowl 50. This bowl 50, which isrotating component 20′, has cutout 53 and cutout gap 54.

Bowl 50 is metal-injection molded in two parts. Its non-magnetic base 52is molded of X2CrNi1911 steel along with such additives as wax. Acylindrical wall of powdered X12CrNiSi7 steel is then injected aroundit, also combined with such additives as wax in another mold.

The resulting metal-injection molded blank is then at lest partly washedfree of the additives, especially the wax, and “baked” at approximately1000° down to its final dimensions, approximately 30 percent of itsoriginal dimensions, in a process similar to sintering.

Although metal-injection molding (MIM) is in itself known, using it tofabricate parts like the two embodiments of a magnet holder specifiedherein is not.

As specified hereintofore with reference to FIG. 1, angle-of-rotationsensor 2 has a component 20′ in the form of an annular magnet 24 thatrotates around stationary component 20.

In FIG. 6, mutually facing webs 90 and 92, which position the magnetprecisely in relation to the space during assembly, can be made of thesame material as the magnetic component they are mounted on, or ofplastic, and are here mounted on annular magnet 24, which comprisesnorth-south segment 24.1 and south-north segment 24.2. The interior ofone segment is north-poled and its exterior south-poled, the interior ofthe other is south-poled and its exterior north-poled. The overallmagnet is accordingly radially two-poled and acts like a bar magnet. Themagnetic flux is radial in the areas labeled N and S. The only fieldirregularities are at interfaces 24.3 and 24.4, and the webs aresituated in those magnetically neutral regions. The device may on theother hand have only one web 90 or even several webs 91. Annular magnet24 can also be provided with a cut-out gap 94 which aids instabilization.

The radially two-pole annular magnet 24 must be positioned at aspecified angle α, 90° in the illustrated embodiment, to the twomutually facing halves 21.1 and 21.2 of stator 21, which as hereintoforespecified, are in the form of fixed sintered stator halves 70 and 80.

In FIG. 6 one of the webs is utilized to establish annular magnet 24 inthe gap 54 cut out of bowl 50 at angle α.

Additionally in FIG. 6 both webs 90 and 92 are utilized to establishannular magnet 24 in cut-out gaps 64 and 65 at angle α.

It should be emphasized that the webs and matching cut-out gaps allowsimple and extremely precise positioning of annular magnet 24. Nocomplicated re-adjustments are necessary. It is essential to the presentinvention that annular magnet 24 cannot turn inside base 52 or wall 51.Even the most powerful forces cannot displace or remove the magnet.

There has thus been shown and described a novel rotation angle sensorwhich fulfills all the objects and advantages sought therefor. Manychanges, modifications, variations and other uses and applications ofthe subject invention will, however, become apparent to those skilled inthe art after considering this specification and the accompanyingdrawings which disclose the preferred embodiments thereof. All suchchanges, modifications, variations and other uses and applications whichdo not depart from the spirit and scope of the invention are deemed tobe covered by the invention, which is to be limited only by the claimswhich follow.

What is claimed is:
 1. In an angle-of-rotation sensor with a stationarycomponent and a rotating component, wherein the stationary componentincludes a stator, the stator is in two halves of ferritic materialseparated by space, and the rotating component includes an annularmagnet accommodated in a magnet holder rotating around the stator withan airgap between them, the improvements wherein the ferritic statorhalves are sintered stator halves, each said stator half being held by astator holder, each said stator holder being secured in a stabilizingcutout in a baseplate of non-magnetic material, and wherein the magnetholder is metal-injection molded.
 2. The angle-of-rotation sensordefined in claim 1, wherein the stator holders are sintered. 3.Angle-of-rotation sensor defined in claim 1, wherein the baseplate is astator baseplate with at least one stabilizing cutout. 4.Angle-of-rotation sensor defined in claim 1, wherein the statorbaseplate comprises the base of a stationary-component housing and hasstabilizing cutouts with sintered stator halves forced into saidstabilizing cutouts.
 5. Angle-of-rotation sensor defined in claim 1,wherein the stator baseplate is a stabilizing disk with at least onestabilizing cutout and is at least partly surrounded by an annularfastener with at least one fastening cutout, and is surrounded by thebase of the stationary component housing, whereby the sintered statorhalf is fastened to the stator baseplate such that the baseplate restsat least partly against the stabilizing disk.
 6. Angle-of-rotationsensor defined in claim 5, wherein the stabilizing disk is partlysurrounded by the base of the stationary component housing. 7.Angle-of-rotation sensor defined in claim 1, wherein the stabilizingcutouts and the fastening cutouts are round or orange-segment shaped. 8.Angle-of-rotation sensor defined in claim 5, wherein the statorbaseplate is aluminum, copper, or plastic.
 9. Angle-of-rotation sensordefined in claim 4, wherein the base of the housing is of plastic,preferably injection-moldable plastic.
 10. Angle-of-rotation sensordefined in claim 2, wherein the holder is a cup metal-injection moldedin one piece of magnetic material with an essentially round foot, amagnetically insulating section in the form of at least two, preferablycylindrical stems rising out of one edge of the foot, and an essentiallyround and hollow bowl resting on the stems.
 11. Angle-of-rotation sensordefined in claim 2, wherein the holder is metal-injection molded in twoparts, comprising an essentially straight-sided bowl with a magneticallyinsulating section in the form of a round base metal-injection molded ofa non-magnetic material with a cylindrical wall of magnetic materialaround it.
 12. Angle-of-rotation sensor defined in claim 11, wherein thebowl and the wall are provided with at least one cut-out gap. 13.Angle-of-rotation sensor defined in claim 11, wherein the annular magnetis provided with at least one web that engages one of the cut-out gapsin the wall or bowl.
 14. Angle-of-rotation sensor defined in claim 13,wherein the web or webs is or are positioned near at least one of thejoints between the south-north and the north-south segments of theannular magnet.
 15. Angle-of-rotation sensor defined in claim 13,wherein the webs is either of the same material as the magnet they aremounted on or of plastic.
 16. Angle-of-rotation sensor defined in claim11, wherein the magnetic material employed for the wall is a ferrite,especially X12CrNiSi7 steel, that includes at least chrome and nickel.17. Angle-of-rotation sensor defined in claim 11, wherein thenon-magnetic material employed for the base is a ferrite, especiallyX2CrNi1911 steel, that includes at least chrome and nickel.